1. Field of the Invention
The present invention relates generally to devices for the detection of dielectric shift induced capacitive changes. The present invention relates more specifically to the use of such devices for the detection and monitoring of the presence or absence of a person from a medical bed, chair or other support structure so as to insure the safety of a patient occupying such a structure.
2. Description of the Related Art
A problem well known to medical service providers is that of making sure certain patients remain in their medical bed or chair. Reasons for this include the need to quickly locate the patient, administer medical treatment to the correct patient, and the prevention of patient injury. Such knowledge is particularly important when patients have become disoriented due to illness or medication.
Medical bed and chair occupancy monitoring systems have been devised to assist medical providers with monitoring the presence or absence of a person in their bed or chair. Such systems typically are equipped with an alarm or are electronically tied to a common monitoring location, such as a nurses station. Such systems principally use some form of pressure sensitive switch as their key sensing element. U.S. Pat. Nos. 4,484,043 and 4,565,910, both Musick et al, and other similar patents describe switch mechanisms which are used to open and close a circuit to indicate the evacuation of a bed or chair by a patient. In the above described patents, the switch apparatus is housed in a thin rectangular cover which may be placed between the patient and the mattress or between the patient and the seating surface. An alternative version of the above described switch mechanism is placed between the lower surface of the mattress and the upper surface of the bed frame. The switch devices in all of the above described mechanisms are each comprised of two rectangular conductors which run the length of the device, are parallel to each other and lie one on top of the other. The two conductors are separated at both ends by a pliable material such as foam and are held apart from each other through the rigidity of the switching apparatus itself. The switch is activated by the pressure of the patient""s body weight on the device, either directly thereon or indirectly through the mattress. Once this weight is applied, the two conductive elements come into contact, the switch is closed, and the system indicates that the patient is in the bed or chair. When the switch is opened by the absence of the patient""s weight in the bed or chair, the system then sounds an alarm or sends a signal to the medical facility call system through an appropriate interface.
Such pressure sensitive switching elements, as previously described, suffer from certain inherent problems. Switching elements which are placed under the mattress exhibit extremely limited sensitivity and selectivity in identifying the presence of a patient in the bed. This is due to the fact that the patient""s weight in the bed is masked by the mattress itself. This masking effect tends to result in frequent false alarms due to the switch failing to close properly, as well as the failure to generate an alarm when the switch fails to open, even though the patient is no longer in the bed. As for pressure sensitive switches placed between the patient and the mattress or seating surface, they must be extremely thin to afford the patient a reasonable degree of comfort. Although such switches exhibit substantially improved sensitivity and selectivity, the required thinness of the movable switch elements, their supportive structure and the required dielectric space between them causes them to have a considerably limited life. Such switches are, therefore, manufactured as disposable devices whose costs prohibit their broad acceptance and use.
It is, therefore, an object of this invention to provide a proximity induced non-compressive dielectric shift sensing device, which replaces the existing pressure sensitive switches previously described for the monitoring of the presence of a patient in a medical environment. A further object of this invention is to provide such a device which either interfaces with occupancy monitoring control modules already in use or utilizes self-contained control module circuitry and controls.
It is another object of the present invention to provide a proximity induced non-compressive dielectric shift sensing device which may be used as a portable unit, or may be wholly or partly built into or mounted on a medical bed, chair, mattress, cushion or similar structure to sense the presence or absence of a person normally occupying the structure.
It is a further object of the present invention to provide a proximity monitoring device with a limited and controlled range that can reliably detect the presence or absence of a person, thereby decreasing the number of false and unreliable alarms.
It is another object of the present invention to provide a proximity monitoring device which will greatly decrease or eliminate patient discomfort by replacing mechanical pressure sensitive switches in the medical bed or chair with a considerably thinner and more flexible sensing element.
It is a further object of this invention to provide a proximity monitoring device, the sensing element of which will exhibit considerably lengthened service life through the elimination of all moving components within the sensing element.
It is a further object of this invention to provide a proximity monitoring device whose sensing element is inherently simpler in design and to manufacture, and utilizes less raw material, thereby resulting in a lower cost end user product.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
According to the present invention, the foregoing and other objects and advantages are attained by an electronic device able to detect and monitor the presence or absence of a person within a pre-defined space. The device generally comprises a capacitive array housed within a polyester mat or other appropriate nonconductive substrate material which is interconnected with a control module. The control module supplies to the capacitive array a suitable oscillator derived driver current and concurrently senses capacitance value changes within the capacitive array induced through dielectric shifts within the array brought about by the proximity or absence thereof of the patient""s body mass. The monitor/control module generally comprises a power supply, a driver/sensor circuit, a comparator/calibration logic circuit, a system interconnection integrity circuit and an alarm generation circuit. It may also optionally contain a nurse call relay circuit for interconnection to a facilities nurse call system.
The driver/sensor circuit provides and senses a suitable current to the capacitive array located in the patient""s bed or chair. The driver/sensor circuit is connected to and controlled by a comparator/calibration logic circuit that is most preferably microprocessor based. This logic circuit continually analyzes and optimizes signals received from and generated by the driver/sensor circuit. In this way, the logic circuit defines capacitive value parameters which it interprets to indicate whether a patient is in close proximity to the capacitive array or absent from that array. In such manner, the logic circuit determines the presence or absence of a patient from his or her support structure. Should the capacitive value change and remain at a level indicative of a patient""s absence from their support structure, the logic circuit would, after a suitable pre-programmed time delay, instruct an alarm circuit to activate. This alarm activation may consist solely of audible and/or visible alarms on or within the control module or may be directed to a medical facility""s nurse call system through an appropriate interface relay circuit contained either within, or remote to, the control module.
In addition to the above described functions, the logic circuit receives continuous data from the control module system interconnection integrity circuit about the continuity of connection between the control module and the capacitive sensor array and, where appropriate, between the control module and the medical facility""s nurse call system.
The logic circuit may also, if appropriate, continuously monitor the entire system during utilization for service faults and subsequently generate appropriate alarms.
The apparatus of the invention, uses a proximity induced non-compressive dielectric shift sensing mechanism, and thus reliably detects the presence or absence of a patient from a bed, chair or other support structure, with minimal discomfort to the patient and with a greatly extended sensor element service life.
Still other objects and advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein multiple preferred embodiments of the invention are shown and described, simply by way of illustration of the best mode contemplated by the inventor for carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawings and descriptions are to be regarded as illustrative in nature, and not as restrictive.